You can visit Switzerland any time throughout the year. Summer lasts roughly from June to September and offers the most pleasant climate for outdoor pursuits. Unfortunately, you won't be the only tourist during this period, so prices can be high, accommodation hard to find and the mainstream sights crowded. You'll find much better deals and fewer crowds in the shoulder seasons of April-May and late-September-October.
At any time, as you travel around the country you'll hit many different climatic conditions. The continental climate in the Alps tends to show the greatest extremes between summer and winter. Mid-August to late October generally has fairly settled weather, and is a good period for hiking trips.
If you're keen on winter sports, resorts in the Alps begin operating in early December, move into full swing around Christmas, and close down when the snow begins to melt in April.
The mountains are mainly responsible for the variety of local and regional microclimates. Ticino in the south has a hot, Mediterranean climate, but most of the rest of the country has a central European climate. Summer temperatures are typically in the low-to-mid 20°Cs (60-70°F) and between 2°C (36°F) and 6°C (42°F) in winter. Travellers need to be prepared for a range of temperatures dependent on altitude. There is perennial snow cover at altitudes above 3000m (9842ft). Summer is the most pleasant time for outdoor pursuits (with the exception of skiing). Strong winds from the south, known as the Fohn , bring high temperatures (and sometimes red dust from the Sahara) and are a major cause of avalanches.
Source:www.lonelyplanet.com